Even with their rapid motion through the large corridors, their sweat and the extreme humidity combined to form a halo like mist around their heads. They ignored the phenomenon and the darkness behind them, never looking back as they continued deeper into the river-carved canyon.
For the first 8 kilometers (5 miles) it was clear sailing and they made good time. They skimmed over bottomless pools and past forbidding galleries that extended deep into the walls of the caverns. The ceilings in the string of river chambers varied from a high of 30 meters (98 feet) to barely enough room to squeeze the Hovercraft through. They bounced over several small, shallow cascades without difficulty and entered a narrow channel where it took all their concentration to avoid the everpresent rocks. Then they traveled through one enormous gallery that stretched almost 3 kilometers (slightly under 2 miles) and was filled with stunning crystals that glinted and sparkled beneath the aircraft light.
On two different occasions, the passage became flooded when the ceiling merged with the water surface. Then they went through the routine of deflating the Wallowing Windbag until it achieved neutral buoyancy, returned to breathing from their air tanks, and drifted with the current through the sunken passage dragging the flattened Hovercraft and its equipment behind them until they emerged into an open cavern and reinflated it again. There were no complaints over the additional effort. Neither man expected a smooth cruise down a placid river.
To relieve the stress they began giving nonsensical names to the galleries and prominent features. The Fun House, the Wax Museum, Giordino's Gymnasium. A small spout from a cavern wall was labeled Postnasal Drip. The river itself they called the Old Sot.
After traveling through a second submerged passage and reinflating their boat, Pitt observed that the current's pace had quickened by two knots and the river gradient began dropping at a faster rate. Like leaves through a gutter drain, they rushed into the eternal land of gloom, never knowing what dangers lurked around the next bend.
The rapids increased frighteningly as the Hovercraft was suddenly swept into a raging cataract. The emerald water turned a boiling white as it cascaded through a passage strewn with boulders. Now the Wallowing Windbag was rearing up like a rodeo bronco as it surged between the rocks and plunged sickeningly into the next trough. Every time Pitt told himself the rapids couldn't possibly get more violent, the next stretch of river slammed the Hovercraft into a seething frenzy that buried it completely on more than one occasion. But the faithful little craft always shook off the froth and fought back to the surface.
Pitt struggled like a madman to keep the boat on a straight course. If they swung halfway around broadside to the tumult, all chances for survival would have been lost. Giordino grabbed the emergency oars and put his back into keeping the boat steady. They swept around a sharp curve in the river over massive rocks, some partly submerged and kicking up great waves shaped like rooster tails, others rising above the turbulence like menacing monoliths. Several boulders were skinned by the little vessel. Then one rose out of the trough that seemed certain to crush the boat and its occupants. But the outer hull sideswiped the unyielding stone without a puncture and was carried past.
Their ordeals never ceased. They were caught in a swirling eddy like a cork being sucked down a drain. Pitt braced his back against an air-filled support cell to stay upright and pushed the throttle to its stop. The howl of the racing engine was lost in the roar of the rapids. All his will and concentration were focused on keeping the Hovercraft from twisting broadside from the force of the speeding current as Giordino assisted by pulling mightily on the oars.
Lost when Giordino took up the oars, the landing lights had fallen overboard into the froth. Now the only light came from the lamps on their hardhats. It seemed a lifetime had passed before they finally broke clear of the whirlpool and were hurled back into the rapids.
Pitt eased back on the throttle and relaxed his hands on the grips of the control bar. There was no point in fighting the river now. The Wallowing Windbag would go where the surging water threw it.
Giordino peered into the black unknown ahead, hoping to see calmer water. What he saw was a fork in the river that divided the mainstream into two different galleries. He shouted above the tumult, "We're coming to a junction!"
"Can you tell which is the main conduit?" Pitt yelled back.
"The one on the left looks the largest!"
"Okay, pull to port!"
The Hovercraft came terrifyingly close to being smashed against the great mass of rock that split the river and only missed turning turtle by a hair as it was overwhelmed by a giant backwash. The little vessel dug into the turbulence and lurched forward sickeningly, burying its bow under a wall of water. Somehow it regained a level keel before being thrown forward by the relentless current.
For an instant Pitt thought he'd lost Giordino, but then the burly little man rose out of the deep pool filling the inside of the boat and shook his head to clear the dizziness brought on by being spun around like a ball in a roulette wheel. Incredibly, he cracked a smile and pointed to his ears.
Pitt understood. The continuous roar of the rapids seemed to be slackening. The Hovercraft responded to his control again, but sluggishly, because it was half-full of water. The excess weight was making it impossible to maintain an air-cushion. He increased the throttle and yelled to Giordino.
"Start bailing!"
The boat designers had thought of everything. Giordino inserted a lever into a small pump and began shoving it back and forth, causing a gush of water to shoot through a pipe over the side.
Pitt leaned over and studied the depths under his headlamps. The channel seemed more constricted, and although the rocks were no longer churning up the water, the river seemed to be moving at a horrifying speed. Suddenly, he noticed that Giordino had stopped bailing and was listening with an apocalyptic look on his face. And then Pitt heard it too.
A deep rumble boomed from the black void downriver.
Giordino stared at him. "I think we just bought the farm!" he shouted.
The vision of going over Niagara Falls returned. This was no spout from above they were approaching. The sound that reverberated through the cavern was that of an enormous volume of water rushing over an immense cascade.
"Hit the inflator on your buoyancy compensator!" Pitt roared above the chaos.
The water was sweeping them along at a good twenty knots and appeared to be funneling into a concentrated surge. A million liters of water sucked them toward the unseen precipice. They rounded the next bend and sailed into a maelstrom of mist. The thunderous rumble became deafening.
There was no fear, no sense of helplessness, no feeling of despair. All Pitt felt was a strange numbness as if all power of intelligent thought had abruptly evaporated. It seemed to him that he was entering a nightmare where nothing had any shape or form. His final moment of clarity came when the Wallowing Windbag hung suspended for a moment before soaring into the mist.
With no point of reference, there was no sensation of falling, rather, it seemed as if they were flying through a cloud. Then his hold on the control bar was lost and he was hurled out of the Hovercraft. He thought he heard Giordino shout something, but the voice was lost in the roar of the falls. The drop through the vortex seemed to take forever. And then came the impact. He struck a deep pool at the base of the falls like a meteor. The air was driven from his lungs and he thought at first that he was smashed to bloody pulp on rocks, but then he felt the comforting squeeze of water all around him.